1. Field of the Invention
The present invention relates to a pattern forming method capable of easily forming a pattern having excellent resolution on the surface of a solid, an arranged fine particle pattern forming method capable of regularly arranging fine particles patternwise on a substrate, a conductive pattern forming method capable of forming a conductive pattern of silver, copper, or the like that has excellent durability on a substrate in a high density and that is excellent for production, and a conductive pattern material useful for electrical wiring material, electromagnetic wave preventive film, magnetic film, etc.
2. Description of the Related Art
The modification of the surface of a solid with a polymer has been widely studied in industrial fields since surface properties such as wetting, staining, adhesivity, surface friction, and cytotropism of a solid can be changed. Of these surface modification techniques, surface modification with a surface graft polymer involving the direct covalent bonding of a polymer to the surface of a solid is known to have the following characteristics:
i) This surface modification technique is advantageous in that a firm bond is formed between a surface and the graft polymer; and
ii) Characteristic properties can be exhibited that are attributable to a large difference in affinity for material existing between a graft polymer and a polymer formed by ordinary spreading and crosslinking.
Various techniques have been proposed for the application of surface graft polymers having the aforementioned advantages by making the use of their characteristic properties. For example, these surface graft polymers are used in the arts relating to living organisms such as cell cultures, antithrombotic artificial blood vessels and artificial articulation, and the art of hydrophilic film and hydrophilic supports for printing plates requiring surface hydrophilicity.
Further, when such a graft polymer is formed patternwise, properties characteristic to the graft polymer are reflected in the pattern. Thus, graft polymers are used in various arts including printing plate precursor, divisional culturing, and dye image formation.
It is reported by Matsuda et al. in “Journal of biomedical materials research”, 2000, vol. 53, page 584, that a hydrophilic graft pattern formed using a fixed polymerization initiator called “iniferter” fixed to a surface is used as a material for culturing cell divisions. It is also reported by Matsuda et al. in “Langumuir”, 1999, vol. 15, page 5,560, that the adsorption of a dye (toluidine blue) to a graft pattern makes it possible to form a pattern of a visible image.
A technique for a graft polymer pattern obtained by patternwise polymerization of a hydrophilic or hydrophobic monomer in the presence of an iniferter polymerization initiator fixed to surface as well as a technique for obtaining a pattern of dye polymer by graftizing a monomer having a dye structure are reported by Metters, A. T. et al. in “Macromolecules”, 2003, vol. 36, page 6,739.
A technique which comprises attaching an initiator imagewise to a gold substrate with a microcontact printing method, and then allowing the occurrence of atom transfer polymerization (ATRIP polymerization) in the presence of the initiator to form patternwise, for example, a HEMA (hydroxyethyl methacrylate) or MMA (methyl methacrylate) graft polymer that is then used as a resist is reported by C. J. Hawker et al. in “Macromolecules”, 2000, vol. 33, page 597.
A method which comprises anion radical polymerization or cation radical polymerization of a silane compound fixed to a substrate to form a graft pattern is proposed by Ingall et al. in “J. Am. Chem. Soc.”, 1999, vol. 121, page 3,607.
However, the aforementioned methods for preparing a graft pattern on the surface of a solid using iniferter method or atom transfer polymerization method of the related art are disadvantageous in that they require too long a reaction time and thus leave something to be desired in terms of production. The methods using anion radical polymerization or cation radical polymerization, too, are disadvantageous in that they require close control over the polymerization reaction and thus leave something to be desired for production.
It has thus been desired to provide a pattern forming method which comprises modifying the surface of a solid with a graft polymer to obtain an effective surface modified material or highly functional material. However, no methods capable of easily forming a graft polymer pattern within a practical production time have as yet been provided.
A technique for arranging fine particles is important for the performance enhancement of aspects such as surface area, resolution, and density of materials such as catalysts, recording materials, sensors, electronic devices and optical devices. Thus, this technique is under extensive study.
For example, Japanese Patent No. 2,828,374 proposes a particle agglomerating method which comprises developing a liquid dispersion medium of fine particles over a substrate to form a thin liquid layer, and then reducing the thickness of the liquid dispersion medium so that it is equal to or smaller than the particle diameter of the particles and thus cause the fine particles to agglomerate by surface tension. In accordance with the invention disclosed in the above cited patent, a layer of fine particles can be regularly agglomerated on a predetermined region to form a uniform particle-integrated layer. However, this technique is disadvantageous in that it is applied with difficulty for the purpose of arranging fine particles patternwise only in a desired region.
As a technique for arranging fine particles patternwise there is disclosed in Japanese patent application laid-open (JP-A) 2002-273209 a method which comprises patternwise exposure of the surface of an oxide substrate such as TiO2 to light to form a hydrophilic and hydrophobic pattern thereon, and then arranging fine particles according to the pattern. The patterned fine particles obtained according to this method are merely physically adhered to the surface of the substrate and are not fixed to the surface of the substrate and thus can easily leave the substrate when stressed. Thus, this method cannot be applied to devices, etc. This method is also disadvantageous in that particles are adhered also to areas other than the predetermined pattern area. It has thus been desired to provide a method capable of forming a fixed particle pattern having high selectivity.
As another method for arranging fine particles patternwise there is known a patterned particle lamination method using a microstamp as disclosed by G. M. Whitesides in “Advanced Materials”, vol. 8, page 245, 1996. In accordance with this method, polymer particles having a submicron size can be orderly integrated in a desired region. Further, the resulting pattern has high selectivity. However, this method is disadvantageous in that a difficult operation is required involving control over the rate of evaporation of solvent in the preparation of an orderly-integrated particle laminate structure, malting it difficult to prepare a desired pattern. This method is also disadvantageous in that it is not suitable for the formation of a large area pattern for these reasons. This method has a further disadvantage in that the adhesion between the patternwise laminated particles and the substrate is too weak, It has thus been desired to provide a method for the formation of a particle adhered pattern capable of attaining a practically sufficient adhesion.
Various conductive pattern materials have been heretofore used to form circuit boards. Referring to a typical example of such a technique, JP-A-2004-31588 discloses a method which comprises forming a thin layer of conductive material On an insulating material by a known method such as vacuum deposition, subjecting the thin layer to resist treatment, patternwise exposure of the resist to light to remove part of the resist, and then etching the material to form a desired pattern. This method requires at least four steps. In the case where a wet etching process is carried out, a step of disposing waste liquid is needed, making a complicated process necessary.
As another conductive pattern forming method there is known a conductive pattern material comprising a photoresist. This method comprises subjecting a substrate, that is coated with a photoresist polymer or that has a dry film-like photoresist adhered thereto, to exposure with ultraviolet light through an arbitrary photomask to form a lattice-shaped or otherwise shaped pattern. This method is useful for the formation of an electromagnetic wave shield requiring high electrical conductivity.
However, with the recent development of micromachines and the trend for further reduction in the size of super LSI, there has been a growing demand for the reduction in size of these wiring structures to a level as small as nanometers. The related art of metal etching is limited in its capability to reduce the size of wiring structures. Further, it is likely that fine wiring portions will when being worked.
As conductive patterns there have been noted not only continuous thin metal layers but also metal particle patterns obtained by allowing metal particles to be selectively adsorbed to a specific region.
Recently, with the development of an advanced information society, electronic appliances have seen remarkable development. In particular, the development of computer technology that supports the development of an advanced information society is greatly attributed to enhancement of the recording density of magnetic discs, not to mention enhancement of integration of semiconductor LSI. The enhancement of the recording density of magnetic discs requires the minimization of defects in the magnetic medium layer and the enhancement of smoothness of the magnetic medium layer.
To this end, a layer having magnetic metal particles dispersed in the surface of a substrate is used at present. It is further known that the patterning of metal particles makes it possible to enhance the recording capacity. In other words, patternwise formation of a metal particle adhered region has been more important. However, this method involving the formation of a fine metal particle pattern for the purpose of enhancing recording density has the same disadvantage as the aforementioned method for forming a thin metal layer pattern, making it difficult to form a fine metal particle pattern having high resolution.